This invention relates to methods of setting up tooling in rotary cutting equipment for slitting sheet material such as light-gauge metal strip and the like. More particularly, it is directed to tooling set-up methods for slitting equipment wherein a web or strip of sheet material is advanced between axially parallel arrays of rotary knives which cooperatively cut plural continuous parallel longitudinal slits in the strip.
An example of such equipment, to which detailed reference will be made herein for purposes of illustration, is a rotary slitter used in the production of narrow metal strips (e.g. for making products such as shutter or venetian blind slats, radiator fins, etc.) from light-gauge cold rolled aluminum alloy strip. The slitter includes upper and lower axially parallel driven arbors each bearing a number of rotary knives spaced along its length. As the strip to be slit is advanced longitudinally between the arbors, in a direction perpendicular to the plane of the arbor axes, the knives coact to cut a plurality of uniformly spaced longitudinal slits in the strip and thereby to divide the strip into a corresponding plurality of narrow strips of uniform width. These narrow strips may be coiled and/or subjected to subsequent operations such as roll-forming, painting, and cutting to desired final product lengths.
Typically, the arrays of parallel knives are constituted of tooling carried on each arbor and arranged to provide plural radially projecting circular knives spaced apart by gaps along the arbor axis. The projecting knives (herein termed male knives) on each arbor are disposed in register with the gaps (herein termed female knives) on the other arbor, and are slightly shorter in axial length than the famale knives. Thus, with the arbors so positioned that the male knives intersect the major surface planes of the entering work (metal strip), each outer side edge of a male knife on one arbor is juxtaposed in closely proximate but non-interfering relation to an outer side edge of a male knife on the other arbor, for cooperation therewith to cut a slit in the strip.
The attainment of proper cutting action is critically dependent on the axial clearance (spacing along the arbor axes) between each cooperating pair of slit-cutting male knife edges. Accordingly, the axial length of each male and female knife must be controlled within very close tolerances. One way of meeting this tolerance requirement is to provide the complete tooling for each arbor as a single integral preformed unit of alternating male and female knives, fixed or removably mountable on the arbor; such units can be machined to the requisite tolerances, although their production is costly and time-consuming. With integral preformed tooling units, however, the spacing between adjacent slits and also the axial clearance between cooperating pairs of male knife edges are invariable, so that they are usable only as dedicated tooling for the fabrication of a single product, viz. to cut slits of given spacing in strip of a given gauge, hardness and alloy composition. When the same slitting equipment must be used to fill multiple relatively small orders for a variety of different products, necessitating frequent tooling changes, the expense and time required to provide dedicated tooling for each product would be prohibitive.
It is therefore preferred, in many instances, to employ so-called universal tooling comprising a set of separate large-diameter circular cutter and male spacer elements and small-diameter circular collar or female spacer elements that can be individually mounted in desired sequence on an arbor to make up an alternating array of male and female knives, with additional male and/or female spacers provided at the ends of the array. In an illustrative universal tooling set, the cutters are machined to a uniform nominal axial length, while male and female spacers are provided in a multiplicity of different nominal axial lengths; each male knife is constituted of two cutters spaced apart axially by one or more (usually several) male spacers, while each female knife is made up of one or more (again, usually several) female spacers. Slit spacing may readily be varied, at least over a substantial range, by varying the number and/or nominal lengths of the spacers used in the male and female knives. The cutters and spacers, being keyed on an arbor in end-to-end abutting relation to each other, stably maintain the position and length of each male and female knife they comprise. Conveniently, the universal tooling set includes two cutters, and at least two spacers of each nominal axial length, for each slit to be cut.
The provision of requisite close knife-length tolerances with universal tooling has heretofore presented substantial difficulty. It is feasible to machine the individual cutters and spacers to reasonably small axial-length tolerances, but the cost of the tooling increases as the permitted tolerances are reduced. As a general rule, the large multiplicity of these elements constituting a complete universal tooling set will include a substantially equal distribution of elements above and below nominal length, i.e. within the individual length-tolerance limits of the elements. There is, however, no assurance that the particular elements selected to make up the male and female knives on the two arbors of a slitter will exhibit a like distribution. Thus, ordinary set-up procedures may happen to result in a preponderance of above-nominal tooling elements on one arbor and a preponderance of below-nominal elements on the other arbor. Within the practicable limits of individual tooling element tolerances, differences between the accumulated tolerances on the two arbors can readily result in unacceptable failure to achieve the very precise axial clearance required between cooperating pairs of male knife edges; the likelihood such misalignment increases with the number of slits to be cut. To compensate for unbalanced accumulated tolerances in universal tooling set up, it has frequently been necessary to resort to such inconvenient expedients as the use of field-fit thin plastic shims, especially in setting up tooling to cut a substantial plurality of slits.